This invention relates to a controller for controlling a current flowing in a motor by a pulse width modulation inverter, and particularly to a current controller for a motor which is suited to raise the current from zero to a target value in each of a plurality of successive constant time periods, to a method for such control, and to products to which the controller, the motor, and the method are applied.
In conventional current control of a motor, as disclosed in, for example, Japanese Patent laid-open Publication 39892/1986, a reference voltage and an applied voltage proportional to the current flowing in the motor are compared with each other by a comparator, and when the applied voltage exceeds the reference voltage, the current is stopped from flowing; thereafter, the current again flows in the motor after a constant time, that is, the current in the motor is interrupted periodically by an analog circuit using a comparator, resistors and capacitors.
The conventional current controller, which is formed of a comparator, resistors and capacitors, and is changed in its performance by temperature change and so on, needs adjustment and is very complicated in its construction because it consists of a plurality of elements. Moreover, when the conventional current controller is implemented in the form of a microcomputer, a problem of delay due to the conversion time and sampling time in the analog-digital convertor will reduce the quality of the performance or disable the control.